Reinforced carbon nanotubes

ABSTRACT

The present invention relates generally to reinforced carbon nanotubes, and more particularly to reinforced carbon nanotubes having a plurality of microparticulate carbide or oxide materials formed substantially on the surface of such reinforced carbon nanotubes composite materials. In particular, the present invention provides reinforced carbon nanotubes (CNTs) having a plurality of boron carbide nanolumps formed substantially on a surface of the reinforced CNTs that provide a reinforcing effect on CNTs, enabling their use as effective reinforcing fillers for matrix materials to give high-strength composites. The present invention also provides methods for producing such carbide reinforced CNTs.

RELATED APPLICATIONS

[0001] This application claims the benefit of U.S. ProvisionalApplication Serial No. 60/347,808, filed on Jan. 11, 2002, which ishereby incorporated herein by reference in its entirety.

GOVERNMENT SUPPORT

[0002] The present invention was made with partial support from The USArmy Natick Soldier Systems Center (DAAD, Grant Number 16-00-C-9227),Department of Energy (Grant Number DE-FG02-00ER45805) and The NationalScience Foundation (Grant Number DMR-9996289)

FIELD OF THE INVENTION

[0003] The present invention relates generally to reinforced carbonnanotubes, and more particularly to reinforced carbon nanotubes having aplurality of microparticulate carbide materials formed substantially onthe surface of such reinforced carbon nanotubes composite materials.

BACKGROUND OF THE INVENTION

[0004] Reinforcing fillers are usually added to a matrix material toform high-strength composites. In order for the resulting composites tobe useful, the reinforcing fillers must have a high load-bearing abilityand binding affinity for the matrix. Carbon nanotubes (CNTs) have beenadded to matrix materials to form high-strength composites. However, theuse of CNTs as reinforcing fillers, including multi-walled CNTs, hasseveral disadvantages. Multi-walled CNTs have a tendency to pull out of,or slip from the matrix material, resulting in reduced load bearingability. This is attributed to the fact that the interface between thematrix material and nanotube layers is very weak, thereby causing a“sword-in-sheath” type failure mechanism. Typically, only the outermostlayer of multi-wall CNTs contributes to load bearing strength. (See, forexample, D. Qian, et al. Appl. Phys. Lett., 76, 2868 (2000) and C.Bower, et al. Appl. Phys. Lett., 74, 3317 (1999)). Because of the weakvan der Waals interaction between the CNTs cylindrical graphene sheets,improved bonding between carbon nanomaterials such as relatively “inert”CNTs and the matrix material is, therefore, essential for improvedmechanical performance of the composite.

[0005] For high-strength CNT reinforced composites, the matrix materialhas to bind to the CNT reinforcing filler strongly (to prevent the twosurfaces from slipping), so that an applied load (such as a tensilestress) can be transferred to the nanotubes. (See, for example, P.Calvert, Nature, 339, 210 (1999)). Several methods, including chemicalfunctionalization of CNT tubule ends and side walls have been proposedand attempted to enhance bonding between CNTs and matrix material. (See,for example, J. Chen, et al. Science, 282, 95 (1998); A. Grag, et al.Chem. Phys. Lett., 295, 273 (1998), and S. Delpeux, et al. AIP ConfProc., 486, 470 (1999)). However, no significant improvement inmechanical properties has been observed after such modification.Chemical coating of both multi-wall and single-wall CNTs with metals andmetallic oxides have also been reported for applications such asheterogeneous catalysis and one-dimensional nanoscale composites. (See,for example, T. W. Ebbesen, et al. Adv. Mater., 8, 155 (1996), X. Chen,et al. Compos. Sci. Technol., 60, 301 (2000), and L. M. Ang et al.Carbon, 38, 363 ( 2000 )). The bonding between the coating materials andCNTs is, however, not strong enough to result in efficient loadtransfer. Thus, there exists a need in the art to improve theinteraction between CNT reinforcing fillers and matrix materials inorder to confer high mechanical strength to CNT reinforced compositesand enable their commercial use in the manufacture of high-strength,light-weight mechanical and electrical device components.

SUMMARY OF THE INVENTION

[0006] The present invention provides CNTs comprising a plurality ofmicroparticulate carbide or nitride material that provide a reinforcingeffect on the CNT matrix, thereby conferring improved mechanicalproperties in the composite materials comprising them as reinforcingfillers. In particular, the present invention provides microparticulatecarbide reinforced CNTs comprising boron carbide nanolumps formed on thesurface of CNTs. The present invention also provides a method ofproducing microparticulate carbide reinforced CNTs. Specifically, thepresent invention provides the use of microparticulate carbidereinforced CNTs having boron carbide nanolumps formed on the surface ofthe CNTs to enable their use as reinforcing composite fillers inproducing high strength composite materials.

[0007] The load transfer efficiency between a matrix material andmulti-walled CNTs is increased when the inner layers of multi-walledCNTs are bonded to a matrix material. The present invention providesreinforced CNTs having boron carbide (B_(x)C_(y)) nanolumps formedsubstantially on the surface of the CNTs. The B_(x)C_(y) nanolumpsreinforce CNTs by bonding not only to the outermost layer, but also tothe inner layers of the CNTs, and promote the bonding of matrix materialto the inner layers of multi-walled CNTs. The load transfer efficiencyalso increases dramatically when the shape of the CNTs allows for agreater surface area along the CNTs and the matrix material. Boroncarbides of the formula B_(x)C_(y) are covalent bonding compounds withsuperior hardness, excellent mechanical, thermal and electricalproperties. They are therefore excellent reinforcing material for CNTs.The carbide modified CNTs of the invention have superior mechanicalproperties as fillers for matrix materials, enabling the production ofhigh-strength composites.

[0008] The present invention provides the synthesis of B_(x)C_(y)nanolumps on the surface of multi-wall CNTs. In one embodiment, presentinvention uses a solid-state reaction between a boron source materialand pre-formed CNTs to form boron carbide (B_(x)C_(y)) nanolumps on thesurface of CNTs. In a preferred embodiment, the B_(x)C_(y) nanolumps areformed by a solid-state reaction of magnesium diboride (MgB₂) andpre-formed CNTs. The B_(x)C_(y) nanolumps are preferably bonded to theinner layers of multi-wall CNTs. In a preferred embodiment, the bondingbetween the B_(x)C_(y) nanolumps and the CNTs is covalent chemicalbonding. Typically, such covalent chemical nanolumps bonding betweenB_(x)C_(y) and CNTs occurs in the absence of a secondary phase phaseseparation at the interface.

[0009] The present invention also provides methods of using reinforcedCNTs having B_(x)C_(y) nanolumps as reinforcing fillers in composites.The carbide reinforced CNTs of the invention can be used as additives toprovide improved strength and reinforcement to plastics, ceramics,rubber, concrete, epoxies, and other materials, by utilizing of standardfiber reinforcement methods for improving material strength.Additionally, the carbide reinforced CNTs comprising B_(x)C_(y)nanolumps are potentially useful for electronic applications, such asuse in electrodes, batteries, energy storage cells, sensors, capacitors,light-emitting diodes, and electrochromic displays, and are also suitedfor other applications including hydrogen storage devices,electrochemical capacitors, lithium ion batteries, high efficiency fuelcells, semiconductors, nanoelectronic components and high strengthcomposite materials. Furthermore, the methods of the present inventionprovide large scale, cost efficient synthetic processes for producinglinear and branched carbide reinforced CNTs having B_(x)C_(y) nanolumps.

[0010] The carbide-reinforced CNTs of the present invention have severaladvantages over current reinforcing materials known in the art. CNTs arereinforcing filler for composites because of their very high aspectratio, large Young's modulus, and low density. Carbide reinforced CNTsof the invention containing B_(x)C_(y) nanolumps are superiorreinforcing fillers for incorporation within a matrix material becausethe modification of carbon nanotube morphology by the B_(x)C_(y)nanolumps increases the load transfer efficiency between CNTs and thematrix material. The shape modification of CNTs by B_(x)C_(y) nanolumpsprovides a greater CNT surface area that results in stronger adhesion ofthe matrix material, while nanolump bonding to the inner layers ofmulti-wall CNTs allows for a greater load transfer from matrix materialsto CNTs. Although the carbide reinforced CNT materials of the inventionare illustrated with boron carbide (B_(x)C_(y)) as the reinforcingmaterial, it ill be understood by one skilled in the art that othermetallic and non-metallic carbides, metallic and non-metallic nitridesmay be substituted for boron carbide without departing from the scope ofthe invention. Metallic carbides, such as boron carbides, are among thehardest solids known in the art, along with diamond and boron nitride.B_(x)C_(y) has a high melting point, high modulus, low density, largeneutron capture section, superior thermal and electrical properties, andis chemically inert.

[0011] The foregoing and other aspects, features and advantages of thepresent invention will become apparent from the figures, description ofthe drawings and detailed description of particular embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The present invention will be further explained with reference tothe attached drawings, wherein like structures are referred to by likenumerals throughout the several views. The drawings shown are notnecessarily to scale, with emphasis instead generally being placed uponillustrating the principles of the present invention.

[0013]FIG. 1 shows scanning electron microscope (SEM) images ofmulti-wall CNTs. FIG. 1(a) shows multi-wall CNTs before the formation ofB_(x)C_(y) nanolumps. FIG. 1(b) shows multi-wall CNTs after theformation of B_(x)C_(y) nanolumps.

[0014]FIG. 2 shows transmission electron microscope (TEM) images of amulti-wall CNT with B_(x)C_(y) nanolumps. FIG. 2(a) shows a multi-wallCNT at low magnification. FIG. 2(b) shows a multi-wall CNT at mediummagnification.

[0015]FIG. 3 shows images of B_(xC) _(y) nanolumps on a multi-wall CNT.FIG. 3(a) shows a high-resolution transmission electron microscope(HRTEM) image of a B_(x)C_(y) nanolump on a multi-wall carbon nanotube.FIG. 3(b) shows an enlarged image of the upper portion of FIG. 3(a).FIG. 3(c) shows a fast-Fourier transformation (FFT) image of FIG. 3(b).

[0016]FIG. 4 shows high-resolution transmission electron microscope(HRTEM) images. FIG. 4(a) shows the reacted area of a multi-wall carbonnanotube. FIG. 4(b) shows the interface between B_(x)C_(y) nanolumps anda carbon nanotube is sharp and well bonded. FIG. 4(c) shows an epitaxialrelationship between B_(x)C_(y) nanolump and a multi-wall carbonnanotube with a (101) plane perpendicular to the zigzag-type nanotubeaxis.

[0017]FIG. 5 is a schematic drawing illustrating carbon nanotube (CNT)morphologies.

[0018]FIG. 6 shows low magnification TEM photomicrographs of CNTs grownat varying gas pressures. FIG. 6(a) shows CNTs grown at a gas pressureof 0.6 torr. FIG. 6(b) shows CNTs grown at a gas pressure of 50 torr.FIG. 6(c) shows CNTs grown at a gas pressure of 200 torr. FIG. 6(d)shows CNTs grown at a gas pressure of 400 torr. FIG. 6(e) shows CNTsgrown at a gas pressure of 600 torr. FIG. 6(f) shows CNTs grown at a gaspressure of 760 torr.

[0019]FIG. 7 shows high magnification TEM photomicrographs of CNTs grownat various gas pressures. FIG. 7(a) shows CNTs grown at a gas pressureof 0.6 torr. FIG. 7(b) shows CNTs grown at a gas pressure of 200 torr.FIG. 7(c) shows CNTs grown at a gas pressure of 400 torr. FIG. 7(d)shows CNTs grown at a gas pressure of 760 torr.

[0020]FIG. 8 shows SEM photomicrographs of symmetrically branched(Y-shaped) CNTs. FIG. 8(a) shows symmetrically branched (Y-shaped) CNTsat low magnification (scale bar=1 μm). FIG. 8(b) shows symmetricallybranched (Y-shaped) CNTs at high magnification (scale bar=200 nm).

[0021]FIG. 9 shows TEM photomicrographs branched CNT Y-junctions. FIG.9(a) shows branched CNT Y-junctions with straight hollow arms anduniform diameter (scale bar=100 nm). FIG. 9(b) shows branched CNTY-junctions with a pear-shaped particle cap at tubule terminal (scalebar=100 nm) (expanded in bottom inset) and XDS photomicrograph (topright inset) showing composition of particle. FIG. 9(c) shows branchedCNT Y-junctions shows a branched CNT with a double Y-junction (scalebar=100 nm) (open tubule shown in inset). FIG. 9(d) shows branched CNTY-junctions shows a high resolution partial image of a well graphitized,hollow tubule Y-junction.

[0022]FIG. 10 shows SEM photomicrographs of CNTs grown at various gaspressures. FIG. 10(a) shows CNTs grown at a gas pressure of 0.6 torr.FIG. 10(a) shows CNTs grown at a gas pressure of 50 torr. FIG. 10(c)shows CNTs grown at a gas pressure of 200 torr. FIG. 10(d) shows CNTsgrown at a gas pressure of 400 torr. FIG. 10(e) shows CNTs grown at agas pressure of 600 torr. FIG. 10(a) shows CNTs grown at a gas pressureof 760 torr.

[0023] FIGS. 11 (a-c) show low magnification TEM photomicrographs of“bamboo-like” CNTs synthesized at various temperatures. FIG. 11(a) showsCNTs synthesized at 800° C. FIG. 11(b) shows CNTs synthesized at 950° C.FIG. 11(c) shows CNTs synthesized at 1050° C. FIG. 11(d) shows CNT yielddependence on reaction temperature.

[0024]FIG. 12 shows high-resolution TEM photomicrographs of“bamboo-like” CNTs synthesized at various temperatures. FIG. 12(a) shows“bamboo-like” CNTs synthesized at 650° C. FIG. 12(b) shows “bamboo-like”CNTs synthesized at 800° C. FIG. 12(c) shows “bamboo-like” CNTssynthesized at 1050° C.

[0025]FIG. 13 is a scanning electron micrograph (SEM) image ofreinforced CNT materials with surface bound Magnesium oxide (MgO)showing epitaxial growth of MgO nanostructures on CNT tubules.

[0026]FIG. 14 shows reinforced CNT materials with surface boundamorphous boron oxide (B₂O₃) nanolumps on multi-walled CNT tubules.

[0027] While the above-identified drawings set forth preferredembodiments of the present invention, other embodiments of the presentinvention are also contemplated, as noted in the discussion. Thisdisclosure presents illustrative embodiments of the present invention byway of representation and not limitation. Numerous other modificationsand embodiments can be devised by those skilled in the art which fallwithin the scope and spirit of the principles of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0028] The present invention provides CNTs comprising a plurality ofmicroparticulate carbide materials that exist substantially on the CNTsurface and function as effective reinforcing agents. Specifically, thepresent invention provides reinforced CNTs having a plurality ofmicroparticulate carbide nanolumps formed in situ on the surface of theCNTs. The present invention also provides a method of producingreinforced CNTs having B_(x)C_(y) nanolumps formed on the surface of theCNTs. The present invention also provides a method of using reinforcedCNTs having B_(x)C_(y) nanolumps formed on the surface of the CNTs asreinforcing composite fillers.

[0029] The terms “boron carbide nanolump” and “B_(x)C_(y) nanolump”refer to a nanoscale aggregate comprising a boron carbide microparticleson a surface of a nanoscale carbon material, including but not, limitedto carbon nanotubes. Nanolumps are typically irregular in shape.

[0030] The term “reinforced carbon nanotube” refer to strengthened CNTsin which more force or effectiveness is given to the carbon nanotube. Inone embodiment of the present invention, CNTs are reinforced by reducingthe amount that the inner layers of a multi-walled CNT slip from theouter layers of the CNT. In a currently preferred embodiment, CNTs arereinforced by bonding a microparticulate carbide material substantiallyto the surface of the CNT which binds to the inner walls of the CNTs.

[0031] The term “matrix material” refers to any material capable offorming a composite with reinforced CNTs. Examples of matrix materialsinclude, but are not limited to, plastics, ceramics, metals, metalalloys, rubber, concrete, epoxies, glasses, polymers, graphite, andmixtures thereof. A variety of polymers, including thermoplastics andresins, can be used to form composites with the reinforced CNT's of thepresent invention. Such polymers include, but are not limited to,polyamides, polyesters, polyethers, polyphenylenes, polysulfones,polycarbonates, polyacrylites, polyurethanes or epoxy resins.

[0032] The term “carbide forming source” refers to any suitable materialcapable of forming a carbide material. The carbide forming source can bemetallic or non-metallic. Preferred carbide forming source include, butare not limited to, magnesium diboride (MgB₂), aluminum diboride (AlB₂)calcium diboride (CaB₂), and gallium diboride (GaB₂). Preferably thecarbide forming source exists in the form of a carbide forming sourcepowder.

[0033] A “carbide material” as referred to herein is afforded themeaning typically provided for in the art. More specifically, a carbidematerial is a binary solid compound of carbon an another element.Element capable of forming carbide materials can be metallic ornon-metallic. Examples of element that can form carbides include, butare not limited to, boron (B), calcium (Ca), tungsten (W), silicon (Si),nobium (No), titanium (Ti), and iron (Fe). Carbides can have variousratios between carbon and the element capable of forming carbidematerial. A presently preferred carbide material of the presentinvention is boron carbide (B_(x)C_(y)). A presently preferred carbidematerial of the present invention is boron carbide (B_(x)C_(y)).

[0034] The carbide materials on the surface of CNTs can be either in theform of a contiguous coating layer or a non-contiguous surface layer,such as, for example, in the form of nanolumps. In a preferredembodiment, the carbide material is B_(x)C_(y) in a non-contiguoussurface layer in the form of nanolumps. In one embodiment, the interfacebetween B_(x)C_(y) nanolumps and CNTs is sharp, in which there is noamorphous layer in between the B_(x)C_(y) nanolumps and CNTs. TheB_(x)C_(y) nanolumps may be chemically bound to the CNT surface bycovalent bonding or by van der Waals type attractive forces. Preferably,the B_(x)C_(y) nanolumps are bound to CNTs covalently.

[0035] The B_(x)C_(y) nanolumps of the present invention typically havean average particle size from about 10 nanometers (nm) to about 200 nm.Preferably, the B_(x)C_(y) nanolumps have an average diameter of abouttwo to three times the average diameter of CNTs. In one embodiment, theB_(x)C_(y) nanolumps have an average diameter ranging from about 50 nmto about 100 nm. In a preferred embodiment, the B_(x)C_(y) nanolumpshave an average diameter of about 80 nm.

[0036] The B_(x)C_(y) lump density on the reinforced CNTs of theinvention can vary over a wide range. Preferably, the nanolumps areisolated nanolumps. The spacing variation between adjacent nanolumps ona CNT can range from about 30 nm to about 500 nm and is dependent on theparticle density on the CNT surface, which is expressed as a ratio ofthe percentage of boron atoms to carbon atoms in the boron carbideB_(x)C_(y) (atom % carbon). In a preferred embodiment, the spacingbetween B_(x)C_(y) nanolumps is from about 50 nm to about 100 nm.

[0037] The B_(x)C_(y) nanolumps in the reinforced CNTs of the presentinvention can be crystalline or amorphous. In a preferred embodiment,the B_(x)C_(y) nanolumps are crystalline. The crystal geometries of theB_(x)C_(y) nanolumps include, but are not limited to, rhombohedral,tetragonal and orthorhombic. In a preferred embodiment, the crystalstructure of the B_(x)C_(y) nanolumps is rhombohedral.

[0038] The ratio of boron to carbon in the B_(x)C_(y) nanolumps isvariable. Boron carbides typically exists as stable single phase, with ahomogeneity ranging from about 8 atom % carbon to about 20 atom %carbon. Examples of boron carbon ratios within this range are B₄C andB₁₀C. The boron carbide nanolumps in the reinforced CNTs of theinvention have the general formulas B_(x)C_(y) wherein x ranges from4-50 and y ranges form 1-4. The most stable B_(x)C_(y) structures arerhombohedral with a stoichiometry of B₁₃C, B₁₂C₃ or B₄C, tetragonal witha stoichiometry of B₅₀C₂, B₅₀C, B₄₈C₃, B₅₁C, B₄₉C₃, or orthorhombic witha stoichiometry of B₈C. Other stable B_(x)C_(y) structures include B₁₂C,B₁₂C₂ and B₁₁C₄. In one embodiment, the ratio of boron to carbon is 4boron atoms to one carbon atom (B₄C).

[0039] Typically, twin boundaries can be observed in B₄C nanolumps. Inone embodiment, the twin boundary is along either (101) or (01{overscore(1)}) planes, as shown in FIG. 3(d).

[0040]FIG. 3 shows images of B_(x)C_(y) nanolumps on a multi-wall CNTs.FIG. 3(a) shows an HRTEM image of a B_(x)C_(y) nanolump on a multi-wallcarbon nanotube. FIG. 3(b) shows an enlarged image of the upper portionof FIG. 3(a). FIG. 3(c) shows a FFT image of FIG. 3(b). The simulatedimage, as shown in the inset of FIG. 3(b), and the indexing of the FFTimage, as shown in FIG. 3(c), were carried out by using structuralparameters of B_(x)C_(y) and zone axis of ({overscore (1)}11). FIG. 3(d)shows the twin boundaries along (101) or (01{overscore (1)}) planes ofB_(x)C_(y). The main parameters for the simulated image, as shown in theinset of FIG. 3(b), are: spherical aberration coefficient=0.5 mm,thickness=10 nm, and defocus=50 nm.

[0041] B_(x)C_(y) nanolumps of the invention provide materials such ascarbon fibers and CNTs with a knotted-rope-shaped or bone-shapedmorphology. Knotted-rope-shaped CNTs and bone-shaped CNTs can beexcellent reinforcing fillers to increase strength and toughness due toa more effective load transfer between CNTs and matrix materials. Thelumps or knots allow for mechanical matrix-CNT interlocking.

[0042] Another aspect of the present invention is a method of producingCNTs having boron carbide (B_(x)C_(y)) nanolumps formed on the surfaceof the CNTs. The method of the present invention can be applied to CNTscomprising any morphology including aligned or non-aligned lineararrays. Preferably, the CNTs have a branched, multi-walled morphology.

[0043] The term “carbide forming source” refers to metallic ornon-metallic material, known in the art, capable of forming a carbidein-situ on the CNT surface. Examples of a carbide forming sourceinclude, but are not limited to, Magnesium diboride (Mg B₂), aluminumdiboride (AlB₂), calcium diboride (CaB₂) and gallium diboride (GaB₂). Apreferred carbide forming source is Magnesium diboride (Mg B₂).

[0044] B_(x)C_(y) nanolumps can be grown on CNTs using any suitablemethod. In one embodiment, B_(x)C_(y) nanolumps are grown on CNTs byusing a solid state reaction between a boron source and CNTs. Anysuitable boron source known in the art can be used. Suitable boronsources include, but are not limited to, magnesium diboride (MgB₂) andaluminum diboride (AlB₂). In a preferred embodiment, the boron source isMgB₂. Preferably, the boron source is in the form of a powder. In oneembodiment, the powder comprises particles with an average grain size ofabout 0.1 micrometer (μm) to about 100 micrometers (μm). Preferably, thepowder comprises particles with an average grain size of about 1micrometer. The synthesis of magnesium diboride (MgB₂) powders isaccomplished by combining elemental magnesium and isotopicaly pure boronby known methods.

[0045] The boron source used in the present invention decomposes at atemperature of between about 100° C. to about 1000° C., preferably, at atemperature of about 600° C. Thermally decomposed boron is typicallymore reactive chemically; the solid-state reaction can, therefore, beperformed at relatively low temperatures. In one embodiment, the solidstate reaction is performed at temperatures ranging from about 500° C.to about 2000° C. In a preferred embodiment, the solid state reaction isperformed at temperature of ranging from about 1000° C. to about 1250°C.

[0046] The CNTs used for producing reinforced CNTs of the presentinvention are purified by any suitable method known in the art prior tointroduction of B_(x)C_(y) nanolumps. In one embodiment, CNTs arepurified by washing with a mineral acid. Examples of suitable mineralacids include, but are not limited to, hydrofluoric acid (HF),hydrochloric acid (HCl), hydrobromic acid (HBr), hydroiodic acid (HI),sulfuric acid (H₂SO₄) or nitric acid (HNO₃). In a preferred embodiment,the mineral acid is HCl and HNO₃.

[0047] The purified CNTs nanotubes are then be mixed with the boronsource powder. Gentle mechanical mixing following which the mixture iswrapped with a metal foil to form an assembly. Preferred metal foilsinclude, but are not limited to, transition metal foils. In a currentlypreferred embodiment, the metal foil is Tantalum (Ta). The assembly isthen placed in a ceramic tube furnace, in a vacuum of about 0.5 torr bymechanical pump. In one embodiment, the reaction area is localized onlyat the area where boron is present. That is, no surface diffusion ofboron is observed in the solid-state reaction.

[0048] Alternate methods for the formation of B_(x)C_(y) nanolumps suchas chemical vapor deposition (CVD) can be used. In one embodiment of thepresent invention, CVD of boron carbide such as plasma enhanced chemicalvapor deposition (PECVD), hot filament chemical vapor deposition(HFCVD), and synchrotron radiation chemical vapor deposition (SRCVD)using reactive gas mixtures such as BCl₃—CH₄—H₂, B₂H₆—CH₄—H₂, B₅H₉—CH₄,BBr₃—CH₄—H₂, C₂B₁₀H₁₂, BCl₃—C₇H₈—H₂, B(CH₃)₃ and B(C₂H₅)₃ are used. Oneembodiment, of the present invention uses a solid state reaction betweena carbide forming source and CNTs. Another embodiment, of the presentinvention uses a solid state reaction between a boron source and CNTs.

[0049] The present invention provides a method of manufacturingreinforced carbon nanotubes having a plurality of boron carbidenanolumps formed substantially on a surface of pre-formed CNTscomprising the steps of: (1) purifying a plurality of carbon nanotubesby washing with a mineral acid; (2) mixing the plurality of carbonnanotubes with a boron source powder to form a mixture of carbonnanotubes and boron source powder; (3) wrapping the mixture of carbonnanotubes and boron source powder within a metal foil; (4) placing themetal foil containing the mixture of carbon nanotubes and boron sourcepowder in a ceramic tube furnace; (5) pumping the ceramic tube furnaceto below about 0.5 torr by a mechanical pump; and (6) heating theceramic tube furnace.

[0050] In one aspect of the present invention, a material comprising aplurality of reinforced carbon nanotubes having a plurality of boroncarbide nanolumps formed substantially on the surface of the CNTs isused as reinforcing fillers for materials comprising the step ofcombining the plurality of reinforced carbon nanotubes and a matrixmaterial to form a high-strength composite.

[0051]FIG. 1(a) shows a SEM image of the CNTs before the growth of boroncarbide nanolumps. FIG. 1(b) shows a SEM image of B_(x)C_(y) nanolumpson the surface of multi-wall carbon nanotubes. The B_(x)C_(y) nanolumpsform into a desired morphology, individual nanoparticles instead of ahomogeneous layer on the surface of multi-wall carbon nanotubes. Theaverage particle size of the B_(x)C_(y) nanolumps is about 80 nm indiameter, which is two or three times of the average diameter of CNTs.The lump density on a carbon nanotube varies dramatically, with aspacing variation between adjacent nanolumps from about 30 nm to about500 nm.

[0052]FIG. 2(a) and FIG. 2(b) show TEM images of B_(x)C_(y) nanolumps onmulti-wall CNTs at low and medium magnifications, respectively. Theaverage particle size shown in FIG. 2(a) is about 50 nm, smaller thanthat shown in FIG. 2(b). As shown in FIG. 2(a) and FIG. 2(b), thereaction between boron and CNTs is confined and the main structure ofmulti-wall CNTs remains unchanged. X-ray energy dispersive spectrometer(EDS) analysis on the composition of the nanolumps shows that thenanolumps contain only carbon. No magnesium (Mg) or Boron (B) weredetected. The Mg from the decomposition of magnesium diboride (MgB₂)becomes vapor at the reaction temperature of about 1100° C. to about1150° C. and was pumped out. But the existence of boron can not beexcluded because boron can not be detected by the EDS system, since thelow energy x-rays from boron atoms were absorbed by detector.

[0053]FIG. 4(a) shows an interface between B_(x)C_(y) nanolump andmulti-wall carbon nanotube. Part of multi-wall CNTs is reacted withboron by a solid state reaction, therefore no lattice fringes of CNTscan be observed at the bottom portion of the B_(x)C_(y) nanolump. Thesolid state reaction area is localized only at the area where there isboron. No surface diffusion of boron is observed in the solid-statereaction. As shown by the HRTEM images of FIG. 4(a) and FIG. 4(b), theinterface between B_(x)C_(y) nanolumps and CNTs is sharp. No amorphouslayer was found at the interface between B_(x)C_(y) nanolumps and CNTs.An epitaxial relationship between CNTs and B_(x)C_(y) nanolumps is shownin FIG. 4(c) and supports the conclusion of strong interface betweenB_(x)C_(y) nanolumps and CNTs. Inner layers of CNTs at the reaction areaare also bonded to B_(x)C_(y) as shown in FIG. 4(a) and FIG. 4(b). Thebonding between B_(x)C_(y) nanolumps and CNTs is strong, most likely, acovalent bonding, because the bonding between boron atoms and carbonatoms inside B_(x)C_(y) is covalent.

[0054] The strong bonding at the interface between B_(x)C_(y) nanolumpsand CNTs can prevent the breaking at the interface between B_(x)C_(y)nanolumps and CNTs during load transfer. Bone-shaped short fibers werereported to be ideal reinforcing fillers to increase strength andtoughness due to a more effective load transfer. Therefore, themodification of CNT morphology by B_(x)C_(y) nanolumps increases theload transfer between nanotubes and matrix. Moreover, inner layers ofmulti-wall CNTs are also bonded to B_(x)C_(y) nanolumps, so the innerlayers can also contribute to load carrying, instead of only the outmostlayer.

[0055] Reinforced CNTs can be used to form or reinforce composites withother materials, especially a dissimilar material. Suitable dissimilarmaterials include, but are not limited to, metals, ceramics, glasses,polymers, graphite, and mixtures thereof. Such composites may beprepared, for example, by coating the reinforced CNTs with thedissimilar material either in a solid particulate form or in a liquidform. A variety of polymers, which include but are not limited to,thermoplastics and resins can be utilized to form composites with theproducts of the present invention. Such polymers include, but are notlimited to, polyamides, polyesters, polyethers, polyphenylenes,polysulfones, polyurethanes or epoxy resins. Branched CNTs of thepresent invention can find application in construction of nanoelectronicdevices and in fiber-reinforced composites. The Y-junction CNT fibers ofthe invention are expected to provide superior reinforcement tocomposites compared to linear CNTs.

[0056] The carbon nanotubes comprised in the reinforced CNTs of thepresent invention can possess any of the several known morphologies.Examples of known CNT morphologies include, but are not limited to,linear, non-linear, branched, “bamboo-like”, and non-linear(“spaghetti-shaped”). Individual tubules of such CNTs can be eithersingle or multi-walled. CNTs with the above morphologies are described,for example, in Li, et al., Appl. Phys. A: Mater. Sci. Process, 73, 259(2001) and U.S. application Ser. No. 10/151,382, filed on May 20, 2002.Both references are hereby incorporated herein by reference in theirentirety. In a currently preferred embodiment, the reinforced CNTs ofthe invention have a branched, multi-walled tubule morphology.

[0057] The CNTs in the carbide reinforced CNT materials of the presentinvention can be aligned or non-aligned. Preferably, the CNTs arenon-aligned, substantially linear, concentric tubules with hollow cores,or capped conical tubules stacked in a bamboo-like arrangement.Referring to FIG. 5, the nanotube morphology can be controlled bychoosing an appropriate catalyst material and reaction conditions.Depending on the choice of reaction conditions, relatively largequantities (kilogram scale) of morphologically controlled CNTssubstantially free of impurity related defects, such as for example,from entrapment of amorphous carbon or catalyst particles, can beobtained. The linear CNTs obtained by the methods of the presentinvention have diameters ranging from about 0.7 nanometers (nm) to about200 nanometers (nm) and are comprised of a single graphene layer or aplurality of concentric graphene layers (graphitized carbon). Thenanotube diameter and graphene layer arrangement may be controlled byoptimization of reaction temperature during the nanotube synthesis.

[0058]FIG. 6 shows low magnification TEM images of linear CNTs grown atlow, intermediate and high gas pressures. The low magnification TEMimages of linear CNTs of FIG. 6 are indicative that tubule morphologycan be controllably changed by choice of gas pressure “feeding” into areactor for CNT preparation. The control of gas pressures in the methodsof the present invention is accomplished by regulating gas pressure ofthe gases feeding in to the reactor using conventional pressureregulator devices. FIG. 6(a) shows CNTs grown at a gas pressure of about0.6 torr. CNTs grown at a gas pressure of about 0.6 torr predominantlyhave a morphology that consists of a tubular configuration, completelyhollow cores, small diameter, and a smooth surface. FIG. 6(b) shows CNTsgrown at a gas pressure of about 50 torr. CNTs grown at a gas pressureof about 50 torr have a morphology that is essentially similar to thatat about 0.6 torr, except that a small amount of tubules have an endcapped conically shaped stacked configuration (“bamboo-like”). FIG. 6cshows CNTs grown at a gas pressure of about 200 torr. The CNTs grown ata gas pressure of about 200 torr have a morphology of predominantly theend-capped, conical stacked configurations (“bamboo-like”) regardless ofthe outer diameters and wall thickness of the CNTs. As shown in FIG.6(c), the density of the compartments within individual tubules of theCNTs is high, with inter-compartmental distance inside the “bamboo-like”structures ranging from about 25 nm to about 80 nm.

[0059] At gas pressures greater than about 200 torr, an entirely“bamboo-like” morphology is obtained for the CNTs, with increasedcompartmental density. The inter-compartmental distances within theindividual CNTs decrease with increasing gas pressure (about 10 nm toabout 50 nm at about 400 torr and about 10 nm to about 40 nm at about600 torr and about 760 torr, respectively). As shown in FIG. 6(f), CNTssynthesized at about 760 torr have a wider tubule diameter of about 20nm to about 55 nm. CNTs synthesized at about 760 torr have thin wallsand smooth surfaces. In comparison to linear CNTs synthesized at a gaspressure of about 200 torr, CNTs synthesized at higher pressures ofabout 400 torr and about 600 torr are highly curved and have brokenends, as shown in FIG. 6(d) and FIG. 6(e). The highly curved and brokenends are attributed to fracturing of the CNTs during the TEM specimenpreparation, which is indicative that CNTs with a “bamboo-like”morphology may be readily cleaved into shorter sections compared to thetubular type.

[0060] CNTs of the present invention have a relatively high degree ofgraphitization (process of forming a planar graphite structure or“graphene” layer). The complete formation of cytstalline graphenelayers, and the formation of multiple concentric layers within eachtubule and hollow core, with minimal defects (such as defects typicallycaused by entrapment of non-graphitized, amorphous carbon and metalcatalyst particles) is an important prerequisite for superior mechanicalproperties in CNTs.

[0061]FIG. 7 shows TEM photomicrographs detailing morphologies of linearCNTs grown at different gas pressures. As shown in FIG. 7, CNTs grown atpressures between about 0.6 torr to about 200 torr have goodgraphitization, in which the walls of the CNTs comprise about 10graphene layers which terminate at the end of the CNT that is distalfrom the substrate (i.e., the fringes are parallel to the axis of theCNT), and possess completely hollow cores. Linear CNTs grown at about200 torr have tubule walls comprising about 15 graphene layers.Individual tubules are “bamboo-like” rather than completely hollow, withdiaphragms that contain a low number (less than about 5) of graphenelayers. Graphene layers terminate at the surface of the CNTs, with theangle between the fringes of the wall and the axis of the CNT (theinclination angle) being about 3°,as shown in FIG. 7(b). FIG. 7(c) showslinear CNTs grown at intermediate gas pressures (about 400 torr to about600 torr) have a “bamboo-like” structure. A “bamboo-like” structuretypically has more of graphene layers in the walls and diaphragms oftubules (typically about 25 and about 10 graphene layers in the CNTwalls and diaphragms, respectively), but less graphitization (lowercrystallinity) due to a faster growth rate. Despite the lowcrystallinity, graphene layers terminate on the tubule surface withinclination angle of about 6°. As shown in FIG. 7(d), CNTs grown atabout 760 torr have higher graphitization than CNTs grown at about 400torr to about 600 torr, have a “bamboo-like” structural morphologyconsisting of parabolic-shaped layers stacked regularly along thesymmetric axes of the CNTs. The graphene layers terminate within a shortlength along growth direction on the surface of the CNTs resulting in ahigh density of exposed edges for individual layers. As shown in FIG.7(d), the inclination angle of the fringes on the wall of the CNTs isabout 13°. The high number of terminal carbon atoms on the tubulesurface is expected to impart differentiated chemical and mechanicalproperties in the CNTs compared the hollow, tubular type, and render theCNTs more amenable for attachment of organic molecules.

[0062] CNTs can comprise a branched (“Y-shaped”) morphology, referred toherein as “branched CNTs”, wherein the individual arms constitutingbranched tubules are either symmetrical or unsymmetrical with respect toboth arm lengths and the angle between adjacent arms. In one embodiment,the Y-shaped CNTs exist as (1) a plurality of free standing, branchedCNTs attached to the substrate and extending outwardly from thesubstrate outer surface; and (2) one or more CNTs with a branchedmorphology wherein the CNT tubule structures have Y-junctions withsubstantially straight tubular arms and substantially fixed anglesbetween said arms.

[0063] As seen in FIG. 8, branched CNTs can comprise a plurality ofY-junctions with substantially straight arms extending linearly fromsaid junctions. The majority of branched CNTs possess Y-junctions havingtwo long arms that are a few microns long (about 2 μm to about 10 μm),and a third arm that is shorter (about 0.01 μm to about 2 μm). CNTs withY-junctions comprising three long arms (up to about 10 μm), and withmultiple branching forming multiple Y-junctions with substantiallylinear, straight arms can be also obtained by the method of theinvention. As shown in FIG. 8(b), a high magnification SEM micrographshows that the branched CNTs of the invention possess Y-junctions thathave a smooth surface and uniform tubule diameter about 2000 nm. Theangles between adjacent arms are close to about 120°, thereby resultingin branched CNTs that have a substantially symmetric structure.Y-junctions have a substantially similar structural configuration,regardless of the varying tubule diameters of the CNTs.

[0064] As shown in FIG. 9, Y-junctions of branched CNTs have hollowcores within the tubular arms of branched CNTs. As shown in the inset ofFIG. 9(a), a triangular, amorphous particle is frequently found at thecenter of the Y-junction. Compositional analysis by an x-ray energydispersive spectrometer (EDS) indicates that the triangular particlesconsist of calcium (Ca), silicon (Si), magnesium (Mg), and oxygen (O).The calcium (Ca) and silicon (Si) are probably initially contained inthe catalyst material. It is frequently observed that one of the twolong arms of the Y-junction is capped with a pear-shaped particle (FIG.9(b) and lower inset), that a similar chemical composition as that ofthe aforementioned triangle-shaped particle found within the tubules atthe Y-junction. A trace amount of cobalt (Co) from the catalyticmaterial is found at the surface of such pear-shaped particle. FIG. 9(b)shows that the tubule of the other long arm of the branched CNT isfilled with crystalline magnesium oxide (MgO) from the catalyticmaterial (confirmed by diffraction contrast image in the EDSspectrograph). The upper right inset in FIG. 9(b) shows selected areadiffraction patterns, which indicate that one of the (110) reflections,(101), of the magnesium oxide (MgO) rod is parallel to (0002) reflection(indicated by arrow heads) from carbon nanotube walls. Therefore, themagnesium oxide (MgO) rod axis is along (210). Additionally, Y-junctionsfilled with continuous single crystalline magnesium oxide (MgO) from onearm, across a joint, to another arm can also be obtained. FIG. 12(c)shows a double Y-junction, wherein only one arm of the right-sideY-junction is filled with single crystal MgO. The inset of FIG. 12(b)shows a magnified image of the end of the MgO filled arm, illustratingan open tip that provides entry of MgO into the CNT Y-junctions. FIG.12(d) shows a highly magnified partial Y-junction, which is wellgraphitized, and consists of about 60 concentric graphite layers(partially shown) in its tubule arms, and a hollow core with a diameterof about 8.5 nm. CNTs can comprise a plurality of free standing,linearly extending carbon nanotubes originating from and attached to thesurface of a catalytic substrate having a micro-particulate, mesoporousstructure with particle size ranging from about 0.1 μm to about 100 μm,and extending outwardly from the substrate outer surface. The morphologyof individual CNT tubules can either be cylindrical with a hollow core,or be end-capped, stacked and conical (“bamboo-like”). Bothmorphological forms may be comprised of either a single layer ormultiple layers of graphitized carbon. CNTs can also be separated fromthe catalytic substrate material and exist in a free-standing,unsupported form.

[0065] In another embodiment of the present invention, the reinforcedCNT material comprises a microparticulate oxide material that are boundsubstantially on the surface of the CNT tubules. The microparticulateoxide materials of the invention can be metallic or non-metallic oxides.Examples of oxide materials include, but are not limited to, magnesiumoxide (MgO) and boron oxide (B₂O₃). As shown in FIG. 14 amorphous boronoxide (B₂O₃) nanolumps are formed on multi-walled CNTs. FIG. 14(a) showsa scale bar equal to 100 nanometers. FIG. 14(b) shows a scale bar equalto 200 nanometers. FIG. 14(c) shows a scale bar equal to 10 nanometers.

[0066] CNTs can be grown by any suitable method known in the art. Forexample, multi-wall CNTs can be grown by any CVD method, including butnot limited to, plasma enhanced chemical vapor deposition (PECVE), hotfilament chemical vapor deposition (HFCVD), or synchrotron radiationchemical vapor deposition (SRCVD). Suitable methods for growing CNTs aredescribed by Li, et al., Appl. Phys. A: Mater. Sci. Process, 73, 259(2001) and U.S. application Ser. No. 10/151,382, filed on May 20, 2002,the contents of both these references are hereby incorporated herein byreference in their entireties.

EXAMPLES Example 1 Synthesis of Reinforced CNTs Having Boron Carbide(B_(x)C_(y) ) Nanolumps Formed Substantially on the Surface of the CNTs

[0067] The multi-wall CNTs were grown by catalytic chemical vapordeposition method (see Li, et al., Appl. Phys. A: Mater. Sci. Process,73, 259 (2001), the contents of which is incorporated herein byreference in its entirety) and purified by hydrofluoric acid (HF).Magnesium diboride (MgB₂), a new superconducting material, is used asthe source of boron. The synthesis of magnesium diboride (MgB₂) can besynthesised by combining elemental magnesium and boron in a sealed (Ta)tube in a stoichiometric ratio and sealed in a quartz ampule, placed ina box furnace at a temperature of about 950° C. for about 2 hours.Powder MgB₂ with average grain size of about 1 micrometer decomposes ata temperature of about 600° C. Thermally decomposed boron is morechemically reactive so the solid-state reaction can be performed atrelatively low temperatures. The nanotubes were mixed gently with MgB₂powder first, then wrapped by a tantalum (Ta) foil to form an assembly,and finally the assembly was placed in a ceramic tube furnace, andpumped to below about 0.5 torr by mechanical pump. The sample was heatedat about 1100° C. to about 1150° C. for about 2 hours. Microstructuralstudies were carried out by a JEOL JSM-6340F scanning electronmicroscope (SEM) and JEOL 2010 transmission electron microscope (TEM),respectively. The TEM is equipped with an X-rays energy dispersivespectrometer (EDS). A TEM specimen was prepared by dispersing CNTs intoan acetone solution by sonication and then putting a drop of thesolution on a holey carbon grid.

Example 2 Determining the Composition of B_(x)C_(y) Nanolumps

[0068] In order to find out whether the nanolumps are boron carbide, ahigh-resolution transmission electron microscopic (HRTEM) image of ananolump is taken and shown in FIG. 3(a). The carbon nanotube nature hasbeen preserved after the reaction. The B_(x)C_(y) nanolump iscrystalline. FIG. 3(b) is an enlarged HRTEM image of the top part ofFIG. 3(a). FIG. 3(c) shows a fast-Fourier transformation (FFT) image ofthe HRTEM image shown in FIG. 3(b). The diffraction pattern obtainedfrom FFT (FIG. 3(c)) is indexed as one from zone axis ({overscore(1)}11) of B₄C. Structure parameters of B₄C for the indexing are spacegroup R3m: (166) and lattice parameters, a=0.56 nm, c=1.21 nm. As shownin FIG. 3(b), the simulated HRTEM image using parameters defocus −30 nmand thickness 20 nm also matches with experimental image very well.Although no boron was detected by the EDS analysis, it is reasonable todraw a conclusion that the nanolumps are of the formula, B_(x)C_(y),since both calculated HRTEM image and diffraction pattern match withexperimental ones very well when using structural parameters of B₄C. Theratio between boron and carbon in nanolumps may differ from B₄Cdramatically because boron and carbon atoms can easily substitute eachother. Twin boundaries were often observed in B₄C nanolumps. As shown inFIG. 3(d), the twin boundary is along either (101) or (01{overscore(1)}) planes.

Example 3 Preparation of Catalyst Substrate for Synthesis of Linear CNTs

[0069] Mesoporous silica containing iron nanoparticles were prepared bya sol-gel process by hydrolysis of tetraethoxysilane (TEOS) in thepresence of iron nitrate in aqueous solution following the methoddescribed by Li et al. (Science, (1996), Vol. 274, 1701-3) with thefollowing modification. The catalyst gel was dried to remove excesswater and solvents and calcined for about 10 hours at about 450° C. andabout 10⁻² torr to give a silica network with substantially uniformpores containing iron oxide nanoparticles that are distributed within.The catalyst gel is then ground into a fine, micro-particulate powdereither mechanically using a ball mill or manually with a pestle andmortar. The ground catalyst particles provide particle sizes that rangebetween about 0.1 μm and about 100 μm under the grinding conditions.

Example 4 Preparation of Catalyst Substrate for Synthesis of BranchedCNTs

[0070] Magnesium oxide (MgO) supported cobalt (Co) catalysts wereprepared by dissolving about 0.246 g of cobalt nitrate hexahydrate(Co(NO₃)₂ .6H₂O, 98%) in 40 ml ethyl alcohol, following which immersingabout 2 g of particulate MgO powder (−325 mesh) were added to thesolution with sonication for about 50 minutes. The solid residue wasfiltered, dried and calcined at about 130° C. for about 14 hours.

Example 5 General Synthetic Procedure for Linear CNTs

[0071] The synthesis of CNTs is carried out in a quartz tube reactor ofa chemical vapor deposition (CVD) apparatus. For each synthetic run,about 100 mg of the micro-particulate catalyst substrate was spread ontoa molybdenum boat (about 40×100 mm²) either mechanically with a spreaderor by spraying. The reactor chamber was then evacuated to about 10⁻²torr, following which the temperature of the chamber was raised to about750° C. Gaseous ammonia was introduced into the chamber at a flow rateof about 80 sccm and maintained for about 10 minutes, following whichacetylene at a flow rate of about 20 sccm was introduced for initiateCNT growth. The total gas pressure within the reaction chamber wasmaintained at a fixed value that ranged from about 0.6 torr to about 760torr (depending on desired morphology for the CNTs). The reaction timewas maintained constant at about 2 hours for each run. The catalyticsubstrate containing attached CNTs were washed with hydrofluoric acid,dried and weighed prior to characterization.

Example 6 General Synthetic Procedure for Branched CNTs

[0072] The MgO supported cobalt catalyst of Example 3 were first reducedat about 1000° C. for about 1 hour in a pyrolytic chamber under a flowof a mixture hydrogen (about 40 sccm) and nitrogen (about 100 sccm) at apressure of about 200 Torr. The nitrogen gas was subsequently replacedwith methane (about 10 sccm) to initiate CNT growth. The optimumreaction time for producing branched CNTs was about 1 hour.

Example 7 Characterization of CNT Morphology and Purity by ScanningElectron Microscopy (SEM), and Tubule Structure and Diameter byTransmission Electron Microscopy (TEM)

[0073] Scanning electron microscopy (SEM) for characterization andverification of CNT morphology and purity was performed on a JEOLJSM-6340F spectrophotometer that was equipped with an energy dispersivex-ray (EDS) accessory. Standard sample preparation and analyticalmethods were used for the SEM characterization using a JEOL JSM-6340Fmicroscope. SEM micrographs of appropriate magnification were obtainedto verify tubule morphology, distribution and purity.

[0074] Transmission electron microscopy (TEM) to characterize individualtubule structure and diameter of the CNTs was performed on a JEOL 2010TEM microscope. Sample specimens for TEM analysis were prepared by mildgrinding the CNTs in anhydrous ethanol. A few drops of the groundsuspension were placed on a micro-grid covered with a perforated carbonthin film. Analysis was carried out on a JEOL 2010 microscope. TEMmicrographs of appropriate magnification were obtained for determinationof tubule structure and diameter.

Example 7 Synthetic Procedure for Oxide Reinforced CNTs

[0075] Reinforced CNT materials comprising microparticulate oxide areobtained in a manner substantially similar to the procedure described inExample 1. The oxide source materials used are magnesium oxide (MgO) andboron oxide (B₂O₃). The microparticulate oxide formation on CNTs iscarried out a pressure of 5 torr.

[0076] Although the examples described herein have been used to describethe present invention in detail, it is understood that such detail issolely for this purpose, and variations can be made therein by thoseskilled in the art without departing from the spirit and scope of theinvention.

[0077] All patents, patent applications, and published references citedherein are hereby incorporated herein by reference in their entirety.While this invention has been particularly shown and described withreferences to preferred embodiments thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade therein without departing from the scope of the inventionencompassed by the appended claims.

What is claimed is:
 1. A carbon nanotube material comprising amicroparticulate carbide or oxide material, said microparticulatecarbide or oxide material existing substantially on the surface of saidcarbon nanotube material.
 2. The carbon nanotube material of claim 1,wherein the microparticulate carbide or oxide material existssubstantially as carbide nanoparticles on the surface of the carbonnanotube material.
 3. The carbon nanotube material of claim 1, whereinthe microparticulate carbide or oxide material exists substantially ascarbide or oxide nanolumps on the surface of the carbon nanotubematerial.
 4. The carbon nanotube material of claim 3, wherein thecarbide or oxide nanolumps have an average diameter ranging from 10 to200 nanometers.
 5. The carbon nanotube material of claim 3, wherein thecarbide or oxide nanolumps have an average diameter of about 80nanometers.
 6. The carbon nanotube material of claim 3, wherein thecarbide or oxide nanolumps reside proximally to one another and remainbound to the surface of said carbon nanotube material by physical orchemical bonding.
 7. The carbon nanotube material of claim 6, whereinthe carbide or oxide nanolumps have an inter-particle spacing rangingfrom 30 to 500 nanometers.
 8. The carbon nanotube material of claim 6,wherein the carbide or oxide nanolumps have an inter-particle spacingranging from 50 to 100 nanometers.
 9. The carbon nanotube material ofclaim 1, wherein the microparticulate carbide material is a metallic ora non-metallic carbide.
 10. The microparticulate carbide material ofclaim 9, that is chosen from the group consisting of boron carbide,silicon carbide, magnesium carbide, titanium carbide, and nobiumcarbide.
 11. The microparticulate carbide material of claim 9, that isboron carbide.
 12. The microparticulate carbide material of claim 11,wherein the boron carbide has the formula B_(x)C_(y), wherein x is 4 to50 and y is 1 to
 4. 13. The carbon nanotube material of claim 12,wherein the boron carbide (B_(x)C_(y)) has a stoichiometry selected fromthe group consisting of B₄C, B₁₀C, B₁₃C, B₁₂C₃, B₅₀C₂, B₅₀C, B₄₈C₃,B₅₁C, B₄₉C₃, B₈C, B₁₂C, B₁₂C₂ and B₁₁C₄.
 14. The microparticulatecarbide material of claim 12, wherein the boron carbide has the formulaB₄C.
 15. The carbon nanotube material of claim 1, wherein the oxidematerial is a metallic or non-metallic oxide.
 16. The carbon nanotubematerial of claim 15, wherein the oxide material is magnesium oxide(MgO) or boron oxide (B₂O₃).
 17. The carbon nanotube material of claim1, wherein the carbon nanotube material is a multi-walled carbonnanotube morphology.
 18. The carbon nanotube material of claim 17,wherein a microparticulate carbide material is covalently bonded to themulti-walled carbon nanotube material.
 19. The carbon nanotube materialof claim 1, wherein the microparticulate carbide material exists as astable single phase in a homogeneity ranging from 8 to 20 atom % carbon.20. The carbon nanotube material of claim 1, wherein the carbonnanotubes material have a knotted rope-shaped morphology.
 21. The carbonnanotube material of claim 1, wherein the carbon nanotubes have abone-shaped morphology.
 22. A method of manufacturing a carbon nanotubematerial comprising a microparticulate carbide material, saidmicroparticulate carbide material existing substantially on the surfaceof said carbon nanotube material comprising the steps of: a) contactinga plurality of carbon nanotubes with a mineral acid; b) mixing theacid-treated carbon nanotubes with a carbide forming source material toform a mixture thereof; c) enclosing the mixture of carbon nanotubes andcarbide forming source material within a metallic material; d) placingthe metal material containing the mixture of carbon nanotubes andcarbide forming source material in a heating chamber; e) subjecting theheating chamber to a reduced pressure atmosphere; and f) maintaining theheating chamber at an elevated sufficient to cause formation ofmicroparticulate carbide material on the surface of the carbon nanotubematerial.
 23. The method of claim 22, wherein the carbide forming sourcematerial is a powder.
 24. The method of claim 22, wherein the carbideforming source material is a boron source powder.
 25. The method ofclaim 22, wherein the reduced presure atmosphere is below 0.5 torr. 26.The method of claim 20, wherein the boron source powder is selected fromthe group consisting of magnesium dibromide (MgB₂), aluminum dibromide(AlB₂), calcium dibromide (CaB₂), and gallium dibromide (GaB₂).
 27. Themethod of claim 22, wherein the boron source powder is magnesiumdibromide (MgB₂).
 28. The method of claim 22, wherein the mineral acidis selected from the group consisting of hydrofluoric acid (HF),hydrochloric acid (HCl), hydrobromic acid (HBr), hydroiodic acid (HI),sulfuric acid (H₂SO₄) and nitric acid (HNO₃).
 29. The method of claim22, wherein the mineral acid is nitic acid (HNO₃) or hydrochloric acid(HCl).
 30. The method of claim 22, wherein the metallic material is aTantalum (Ta) foil.
 31. The method of claim 22, wherein the temperatureof the heating chamber is 500° C. to 2000° C.
 32. The method of claim22, wherein the temperature of the heating chamber is 1100° C. to 1150°C.
 33. The method of claim 22, wherein the method comprises a solidstate reaction between a boron source material and the carbon nanotubes.34. The method of claim 22, wherein the microparticulate carbidematerial exists substantially as carbide nanoparticles on the surface ofthe carbon nanotube material.
 35. The method of claim 22, wherein themicroparticulate carbide material exists substantially as carbidenanolumps on the surface of the carbon nanotube material.
 36. The methodof claim 35, wherein the carbide nanolumps have an average diameterranging from 10 to 200 nanometers.
 37. The method of claim 35, whereinthe carbide nanolumps have an average diameter of about 80 nanometers.38. The method of claim 33, wherein the carbide nanolumps resideproximally to one another and remain bound to the surface of said carbonnanotube material by physical or chemical bonding.
 39. The method ofclaim 38, wherein the carbide nanolumps have an inter-particle spacingranging from 30 to 500 nanometers.
 40. The method of claim 38, whereinthe carbide nanolumps have an inter-particle spacing ranging from 50 to100 nanometers.
 41. The method of claim 22, wherein the microparticulatecarbide material is a metallic or a non-metallic carbide.
 42. The methodof claim 41, that is chosen from the group consisting of boron carbide,silicon carbide, magnesium carbide, titanium carbide, and nobiumcarbide.
 43. The method of claim 42, that is boron carbide.
 44. Themethod of claim 43, wherein the boron carbide has the formulaB_(x)C_(y), wherein x is 4 to 50 and y is 1 to
 4. 45. The method ofclaim 44, wherein the boron carbide (B_(x)C_(y)) has a stoichiometryselected from the group consisting of B₄C, B₁₀C, B₁₃C, B₁₂C₃, B₅₀C₂,B₅₀C, B₄₈C₃, B₅₁C, B₄₉C₃, B₈C, B₁₂C, B₁₂C₂ and B₁₁C₄.
 46. The method ofclaim 44, wherein the boron carbide has the formula B₄C.
 47. The methodof claim 22, wherein the carbon nanotube material is a multi-walledcarbon nanotube morphology.
 48. The method of claim 47, wherein themicroparticulate carbide material is covalently bonded to themulti-walled carbon nanotube material.
 49. The method of claim 22,wherein the microparticulate carbide material exists as a stable singlephase in a homogeneity ranging from 8 to 20 atom % carbon.
 50. Themethod of claim 22, wherein the carbon nanotubes material have a knottedrope-shaped morphology.
 51. The method of claim 22, wherein the carbonnanotubes have a bone-shaped morphology.
 52. A method of forming acomposite material comprising a carbon nanotube material and a matrixmaterial, said method comprising the step of combining said carbonnanotube material with a matrix material to form a composite material,wherein the carbon nanotube material comprises a microparticulatecarbide or oxide material.
 53. The method of claim 52, wherein themicroparticulate carbide material exists substantially as carbidenanolumps on the surface of the carbon nanotube material.
 54. Acomposite material comprising a carbon nanotube material and a matrixmaterial, said carbon nanotube material comprising a microparticulatecarbide material.
 55. The composite material of claim 54, wherein themicroparticulate carbide material is substantially on the surface ofsaid carbon nanotube material.